If you’re unfamiliar with the Higgs
boson and LHC, here are five things to know to help you follow this
developing story:

1. The Standard Model and the Higgs boson

The Standard Model is, essentially, an
instructional booklet that describes how subatomic particles and
forces interact. It’s made up of 16 particles total: 12
matter particles and four force-carrier particles.

It’s worked fairly well in the world
of physics so far, but there are some issues that researchers need
to resolve in order to attain a more complete understanding of the
Universe. For one, the Standard Model cannot explain one of the
most fundamental forces out there — gravity. Also, it
describes only ordinary matter which, in the big picture of things,
makes up just a small portion of the total Universe (dark matter is
much more dominant). Then, there’s the Higgs boson
issue.

The Higgs boson, or “God
particle,” is based upon a theory first proposed in 1964
by physicists Peter Higgs, Francois Englert, and Robert Brout. In
it, they stated that particles acquire mass through their
interactions with an all-pervading field, called the Higgs field,
and are carried by the Higgs boson. In other words, the Higgs boson
is responsible for everything in the Universe obtaining mass.
Identifying it is important to the Standard Model because it would
explain why other elementary particles (except photon and gluon)
have mass. Particle masses, and the differences between
electromagnetism and weak force, are significant to many aspects of
the structure of microscopic, and thus macroscopic, matter.

2. The LHC — in a nutshell

The LHC was built by the European Organization
for Nuclear Research in order to test high-energy physics theories
like the Higgs boson. It took more than 15 years to build, with
over 10,000 scientists from 40+ countries contributing to the
effort.

It is, essentially, a “Big Bang
Machine.” The LHC is a Super Proton Synchrotron built in
a tunnel roughly 12.5 feet in diameter that stretches 17 miles in
circumference. It lies several hundred feet below the
France-Switzerland border near Geneva, Switzerland.

The LHC collides two counter rotating beams of
subatomic particles (protons) or lead ions at 99.9999999% the speed
of light, in conditions colder than the space between the stars. By
crashing them together, researchers are able to study the
subsequent release of unstable, high-energy particles.

The proton beams move around the LHC ring inside
continuous vacuum chambers. In order to get them traveling fast
enough, scientists and engineers generate a powerful magnetic field
using 1,740 superconducting magnetics, which needed approximately
40,000 leak-tight welds and 65,000 splices of specially designed
superconducting cables.

In order to avoid excessive resistive losses,
the magnets are kept at just a few degrees above absolute zero.
This is achieved using an enormous, incredibly intricate cryogenics
system: eight above-ground refrigeration plants which, altogether,
pump approximately 400,000 liters of liquid helium a year.

4. Enormous detectors

The LHC proton beams can be stored at high
energy for 10 to 20 hours. Over the course of 10 hours,
they’ll make four hundred million revolutions, with
collisions taking place inside LHC experiment zones, or detectors.
These detectors are capable of pinpointing a particle with an
accuracy of 15 microns; that’s 20 times thinner than a
piece of your hair.

There are six detectors total. They’re
all housed in strategically located, underground caverns. Two
— the ATLAS experiment and Compact Muon Solenoid (CMS)
— are large, general purpose detectors, while A Large Ion
Collider Experiment (ALICE) and LHCb have more specific roles. The
other two, TOTEM and LHCf, are smaller and set up for very specific
research.

A summary and pictures of the four main
detectors:

• ATLAS

Looks for signs of new physics, including
origins of mass and extra dimensions.

Due to their enormity, detectors were assembled
in bits. ATLAS was lowered in pieces over several years, and
assembled almost entirely underground. When its largest part
— the barrel toroid magnet — had to be brought
down a shaft, it had just 10 cm of clearance. And that’s
just the heavy lifting! There was also all of the fine engineering
work that needed to be done in order to actually assemble these
detectors. Layers of electronic sensors were wired and connected by
hand, with up to 300 people a day working in the cave up against
one another.

Meanwhile, the CMS was assembled mostly above
ground in units, including the world’s largest-ever
electromagnet. It took 10 hours to be lowered down a 330-foot
shaft, with a clearance of just 20 cm on either side. Adding to the
stress of this endeavor was the fact that its cylindrically
arranged silicon wafer detectors contain a vast network of
micro-circuitry including 73,000 radiation-hard, low-noise
microelectronic chips, 40,000 analog optical links, and 1,000 power
supply units. One wrong move and the detector could suffer some
fairly severe damage.

So what did the LHC researchers see?

At a seminar yesterday, the heads of ATLAS and
CMS said that they saw “spikes” in their data
at roughly the same mass: 124-125 gigaelectronvolts (GeV). Guido
Tonelli, spokesperson for the CMS detector, summarized the state of
the experiment: “The excess is most compatible with a
Standard Model Higgs in the vicinity of 124 GeV and below, but the
statistical significance is not large enough to say anything
conclusive.

As of today, what we see is consistent either
with a background fluctuation or with the presence of the
boson.”

Further complicating the validity of this story
is that these stats come from just a few events among the billions
of particle collisions that get analyzed at the LHC. The team will
need many more events to occur in order to lend some credence to
this claim.

Regardless though, the possibility that the
Higgs boson might have been
discovered has generated a ton of excitement in the world of
science and engineering. ■